The invention relates to measuring cable travel sensors, and in particular, to cable travel sensors which operate on the basis of a measuring cable principle.
Measuring cable travel sensors comprise a precisely defined and positioned cable drum on to which a measuring cable is wound, generally only in a single layer, and fixed at one end.
The other free end of the measuring cable is secured to the article of which the variation in the position is to be precisely measured.
When the article moves in relative terms away from the cable drum of the measuring cable travel sensor, the angular movements of the measuring cable drum are converted into a precise travel length by means of a rotary angle sensor which is non-rotatably coupled to the measuring cable drum. A rotary torsion spring, which is operatively connected generally in coaxial relationship to the measuring cable drum, ensures that the measuring cable is wound on to the measuring cable drum when the article to be measured moves towards the cable drum.
Measuring cable travel sensors of this kind are used in various technical assemblies, for example, for determining the position of an elevator cabin in an elevator shaft for continuously monitoring the angular position of ailerons or control elevators and vertical rudders in aircraft or the like.
In order to achieve the desired level of measurement accuracy for such measuring cable travel sensors, it is necessary on one hand, to ensure absolute angular truth as between the measuring cable drum and the rotary angle sensor. This requires, inter alia, free unimpeded rotary movement of the measuring cable drum, under all operating conditions, as any impediment to the cable drum would grossly falsify the measurement result. In particular, rubbing of the cable drum against the housing, for example, as a consequence of a mechanical loading, thermal distortion of parts of the housing and so forth, must be avoided.
For this reason the housings of the measuring cable travel sensors have hitherto generally been composed of metal parts. Production using injection molding procedures with plastic material or light metal or alloy has hitherto scarcely been wide-spread by reason of the generally unsatisfactory degree of accuracy and the complicated co-operation of the individual components.
On the other hand the extent of use of measuring cable travel sensors of that kind can be increased in proportion to reduced manufacturing cost thereof and the enhanced universality of the design configuration for example of the means for securing the sensor with respect to a surrounding structure.
An object of the present invention is to provide a measuring cable travel sensor which is inexpensive to produce and which nonetheless functions precisely and which in particular permits a wide variety of possible ways of fixing same with respect to its surroundings.
A further object of the present invention is to provide a method of assembling such a sensor, which permits fast and thus inexpensive assembly of the sensor, thereby to reduce the manufacturing costs of a sensor of that kind in regard to their aspect which depends heavily on the amount of time involved in assembly of the sensor.
These objects are attained by the invention as set forth herein.
Advantageous features and configurations are further set forth in the appendant claims.
As will be apparent from the description hereinafter of a preferred embodiment of the invention the fact that the housing which encloses the mechanical internal space or cavity and which therefore accommodates the cable drum and the flat spiral spring has at least two and preferably four flat outside surfaces which are at a right angle to each other and on each side has one or preferably two mutually parallel outwardly open grooves which are each at the same spacing from the contact edges of the outside surfaces means that the housing and therewith the travel sensor can be fixed in the most widely varying orientations by means of the same clamping claws or brackets to a component of the surroundings, that is with the cable exit of the travel sensor parallel or perpendicular to the component supporting the travel sensor.
If the end faces of the housing also extend at a right angle to the outside surfaces bearing the grooves and screw means which are present in the corners of the housing which is not only rectangular but preferably square as viewed in the longitudinal direction terminate openly visibly in those end faces, then by arranging the nuts on the corresponding screws in corresponding hexagonal recesses in the end faces, it is possible to use nuts into which the corresponding screws which hold the housing together only partially penetrate from the one end, so that other screws are used from the other side, for fixing with respect to the surrounding structure. If then fixing with respect to the surrounding structure is implemented by means of a mounting angle member which, by virtue of arcuate or mutually parallel diagonal slots, permits variability in its angular positioning either with respect to the surrounding component or with respect to the sensor, the most widely varying mounting options can be implemented in a simple fashion.
The internal structure of the travel sensor is also so selected that on the one hand assembly is very simple and quick, while on the other hand production is possible using plastic injection molding, that is to say with the dimensional deviations which necessarily occur in that situation, both in manufacture and also in operational fitment of the sensor.
In that sense the housing which encloses the mechanical internal space for containing the flat spiral spring and the cable drum and which is in the form of a cuboidal portion with a smaller cuboidal portion fitted thereon, more specifically the cable fitment portion through which the cable extends outwardly from the housing in which the cable drum is rotatably disposed, does not as was hitherto conventionally the case comprise two housing portions in the form of half-shell portions, the plane of contact of which extends through the cable fitment portion.
Instead, the housing comprises one mounting plate which accommodates the flat shaped spring and which therefore involves a smaller extent in the longitudinal direction of the travel sensor, that is to say the axial direction of the rotary trunnion or journal of the rotary angle sensor, as already known hitherto, is a cup-shaped mounting plate which however is kept as small as possible in respect of its depth in the longitudinal direction so that this mounting plate, in regard to the cable fitment portion, just also involves a side wall of the latter, while the whole of the remainder of the cable fitment portion is a component part of the other mounting plate which is therefore of a substantially greater longitudinal extent.
Because of its greater axial extent in the longitudinal direction, that other mounting plate is precisely not cup-shaped, that is to say with a closed bottom, but is of such a configuration as to be open at both axial sides or ends. The outwardly directed end face is closed by a separate component which is connected non-rotatably to the rotary angle sensor. As the rotary angle sensor can also be a potentiometer, or pot, that separate component which carries the rotary angle sensor can also be referred to as the pot mounting plate member. This involves advantages in regard to manufacturing procedures, in terms of production tolerances, and also facilitates zero position adjustment of the rotary angle sensor.
In this connection, the screw means, disposed in the four corners of the two mounting plates, can be used in different ways relative to each other, by virtue of the selected radial spacing of the through openings provided for that purpose in the corners of the housing, with respect to the pot mounting plate member.
When using screws without an additional washer, the screw heads no longer project into the region of the pot mounting plate member and they serve exclusively for fixing the two mounting plates relative to each other. This is effected with two screw means which are disposed in diagonally mutually opposite relationship. The other two screw means, which are also disposed in diagonally mutually opposite relationship, are tightened with the interposition of a support washer which is of larger diameter, whereby the pot mounting plate member and therewith also the rotational position of the rotary angle sensor non-rotatably connected thereto is fixed in the desired angular position with respect to the mounting plate.
The pot mounting plate member itself is fixed on the rotary journal or trunnion of the rotary angle sensor not by means of a nut which bears against the end thereof and which acts by force-locking engagement, but rather a positively locking connection is afforded between that nut and the mounting plate by a suitable hexagonal recess in the face of the pot mounting plate member.
In the direction of the free end of the rotary trunnion or journal, the pot mounting plate member is followed by the cable drum which is screwed on the rotary trunnion or journal by means of radially acting clamping screws. In the present case, two clamping screws may be used, which include an angle of 120xc2x0 between them, whereby play-free clamping of the cable drum on the rotary trunnion or journal is possible.
At its free end the rotary trunnion or journal is cut thereinto in the longitudinal direction by a slot to such an extent that the slot can serve directly for inserting and thus positively lockingly fixing the core or center of the flat spiral spring without requiring further aids such as a transverse rivet or the like.
The two parts are brought together after the flat spiral spring is fitted into the spring chamber provided for same in the pot-shaped mounting plate. In this operation, a bar or plate portion at the outer free end of the flat spiral spring is also pushed in the longitudinal direction over a pin or projection which is integrally provided for that purpose on the mounting plate, being therefore injection molded therewith. In this case the flat spiral spring is prefabricated in such a way that, after that fitting operation, the core or center portion of the flat spiral spring is not applied radially outwardly in the spring chamber but remains centrally within the spring, without any fixing.
In this way it is possible, after insertion of the spring, to press into the spring chamber at its end a sliding plate which also comprises plastic material, engaging into a special recess, and fix it in force-locking relationship therein. The force-locking engagement is achieved by an injection-molded burr or ridge which projects deliberately along the periphery of that round sliding plate, by virtue of the plane of contact of the mold halves for that sliding plate being disposed in the central radial plane of the sliding plate. The burr, which is very narrow in the longitudinal direction of the sliding plate, is deformed in the operation of pressing it into a corresponding recess in the mounting plate, to such an extent as to afford secure force-locking fixing in that mounting plate until the two preassembled mounting plates are screwed to each other.
In this respect it is necessary for the one mounting plate unit which includes the rotary trunnion or journal of the rotary angle sensor to be fitted with its projecting slotted free end through the central opening in the sliding plate of the other mounting plate, and there, without being able to see that location, for the slot of the rotary trunnion or journal to be latched into the core or center portion of the rotary spring. This purpose requires good radial pre-adjustment which is initially implemented by virtue of the dimensioning of the central opening in the sliding plate which is only immaterially larger than the diameter of the rotary trunnion or journal. When the components are further fitted together, a flange which projects concentrically in the axial direction on the one mounting plate, more specifically the cable drum mounting plate which is open at both ends, is involved as an additional radial fixing means, insofar as that flange engages into a corresponding recess in the other mounting plate. This radial guidance effect then also makes it possible without difficulty for the two mounting plates to be firstly rotated about the longitudinal axis several times relative to each other prior to screwing of the two mounting plates relative to each other, whereby the flat spiral spring which is accommodated in the housing and which is already non-rotatably connected to the rotary trunnion or pin can be tightened in the necessary fashion.
It is only thereafter that the mounting plates are screwed relative to each other by the above-described first two screw means, followed then by zero position fixing of the rotary angle sensor by suitably turning the pot mounting plate member with respect to the rest of the housing and tightening the other two screw means.
For fixing the measuring cable at its end secured to the cable drum, the cable drum itself, near to the one side flank thereof, has a tangential slot in its winding surface in order to permit the beginning of the measuring cable to pass therethrough in a direction which is as shallowly tangential as possible, while fixing in the internal cavity of the cable drum is effected by clamping a thicker metal tube portion on to the end of the cable, which is thicker than the slot in the winding surface of the cable drum.
The material used for the housing portions is preferably POM 30 or POM G30, that is a plastic material which contains a high proportion of microscopically small glass balls which afford optimum sliding properties with respect to that plastic material relative to the metal elements involved such as the flat spiral spring, the cable drum, the rotary trunnion or journal of the rotary angle sensor and the measuring cable.
As cable drums of different sizes, in particular with respect to diameter can be fitted within one and the same housing, depending on the specific situation of use involved, the cable exit opening in the end face of the cable fitment portion must also be disposed at different locations. For this purpose, no cable exit opening is provided when producing the housing by injection molding, but rather the cable exit opening is subsequently produced at the desired location by boring.
Therefore, as the arrangement does not involve a cable fitment portion constituted by a special, harder, more wear-resistant material than the material of the housing, an acceptably low level of wear of the cable exit opening requires optimum frictional pairing with respect to the measuring cable, as an important consideration. It has been found in this respect that, with housing dimensions of about 3 cmxc3x973 cmxc3x973 cm for the main body of the housing and with the cable fitment portion projecting with respect thereto by about 1 cm and with 10 turns of the measuring cable on the measuring cable drum in mutually juxtaposed relationship in a single layer, a measuring cable of a thickness of between 0.4 and 0.6 mm is the optimum, in particular if that measuring cable comprises either a central wire or strand with between about 15 and 20 twisted strands surrounding it, or 7 strand portions which are twisted relative to each other, one thereof possibly being a central strand, wherein each of the strand portions is in turn produced from between 5 and 8 individual strands in twisted configuration.
It has also been found that the projection distance of the cable fitment portion can be optimized. More specifically, the radial spacing of the cable exit opening with respect to the winding surface of the cable drum can be optimized. In addition, the spring used is a flat shaped spring whose spring characteristic in the working range in which unwinding of the spring is possible extends in a linearly rising configuration.
In the inner end region of the spring characteristic, that is to say upon unwinding of the innermost turns of the flat shaped spring, which is not at all possible by virtue of the limited measuring cable length, in contrast an irregular and steeper configuration for the spring characteristic is acceptable.
In order to prevent unauthorized persons from opening the sensor and in order thereby to avoid possible injury due to the flat shaped spring jumping out, the assembly additionally uses vandal-proof screws, for example socket head screws, slotted screws or cross-slotted screws which cannot be opened with a normal tool because a projection sticks up in the center of the socket opening in the head of the screw, and that means that it is not possible to use a normal wrench for a socket head screw but only a special wrench with a central opening for receiving the projection. The same design configurations are also possible for dealing with cross-slotted screws and normal slotted screws.
For the same reason, the face of the sensor housing, which is remote from the rotary angle sensor, is not primarily intended for fixing the travel sensor, but generally remains free, and is therefore provided with a raised or recessed labelling, which is already formed in the injection molding operation, as a warning against unauthorized opening of the sensor, which is highly recommended for reasons relating to legal liability.
An eye at the free end of the measuring cable is injection molded on to the cable, pressed thereonto or knotted thereto, and preferably comprises high-quality steel, copper or a copper nickel compound.
In addition to the housing which encloses the mechanical internal space, it is possible to fit on to the face from which the rotary angle sensor projects a further cup-shaped housing attachment portion which encloses and protects the rotary angle sensor and in which a circuit board with an electronic evaluation system for the sensor is additionally disposed.
This housing attachment portion can again comprise the same plastic material and can also be produced by injection molding, or, if EMV-security is required, it can be produced from aluminum by extrusion or it can be produced in the form of an aluminum-coated plastic component.
Further objects, features and advantages of the invention will be apparent from the description hereinafter of a preferred embodiment of the invention.